Both fasting and post-prandial GLP-1 levels were significantly lower in subjects with T2DM than those with NGT (2.06 ± 0.43 vs. 2.87 ± 0.67 pg/L, p < 0.01; and 2.49 ± 0.60 vs. 3.42 ± 0.85 pg/L, p = 0.02; respectively). This evidence concerns the gene GCG and type 2 diabetes mellitus.